Wire cable isolator and energy absorbing restraint

ABSTRACT

A wire cable isolator and an associated energy absorbing restraint is provided for connecting between a device subject to movement due to dynamic loads and possibly thermal deflection, and an adjacent structure, such as a building or a support member. The isolator has predetermined, symmetrical force-deflection properties. The isolator includes first and second pairs of entrapment members, and a wire cable formed in a spiral. The first pair of entrapment members clamp the wire cable spiral at opposite side of the spiral and the second pair of entrapment members clamp the wire cable spiral at opposite sides of the spiral. The first and second pair of entrapment members are disposed at predetermined positions about an exterior periphery of the spiral.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 07/978,018, filed Nov. 17, 1992, now U.S. Pat. No. 5,360,210for "Pipe Restraint", which is a continuation-in-part of U.S. patentapplication Ser. No. 915,477, filed Jul. 16, 1992, for "Pipe Restraint",now U.S. Pat. No. 5,240,232, commonly assigned herewith.

TECHNICAL FIELD

This invention relates to energy absorbing restraining devices whichrestrain static and dynamic movement in a spring like manner and dampendynamic movement and more particularly, an isolator for energy absorbingrestraining devices which utilize coiled wire cable for restraining suchstatic and dynamic movement.

BACKGROUND OF THE INVENTION

Energy absorbing restraints can be used in a many applications. Forexample, such restraints are used as restraining devices for processpiping to dampen motion of such piping caused by dynamic events such asfluid transients, flow induced steady state vibrations, earthquakes andthe like.

Additionally, for thermal considerations, piping systems must besupported to allow expansion due to the thermal growth induced by a hotprocess fluid flowing therethrough. Design conflicts occur however,where piping system restraints are necessary to limit dynamicdisplacements at locations along the pipe which also encounter thermalgrowth.

Traditionally this conflict has been resolved by using snubbers whichallow the pipe to freely expand but momentarily restrain the pipe duringa dynamic event. Snubbers, however, absorb little energy, must beperiodically serviced and have been known to fail, resulting in costlysnubber inspection programs, particularly in the nuclear power industry.

Various alternative restraints have been proposed, including gappedrestraints and energy absorbers. Gapped restraints allow free thermaltravel of the piping system, but limit dynamic travel to the limits ofpreset travel constraints. One disadvantage of gapped restraints is thatthey impart high impact loads to the adjoining structure when such arestraint reaches the ends of its travel during a dynamic event.

Several types of energy absorbing restraints are available. One exampleof an energy absorbing restraint is disclosed in U.S. Pat. No.4,620,688, to Khlafallah et al., entitled "Energy Absorbing ApparatusFor Piping System And The Like", which utilizes steel flex plates whichact as a spring. The spring action allows for thermal expansion and alsoabsorbs energy by plastic deformation of the plates during dynamicmovement. Such a restraint, however, has a low cycle fatigue life whichis a significant drawback.

Another type of energy absorbing restraint is disclosed in U.S. Pat. No.4,955,467, to Kallenbach, entitled "Energy Damping Device" whichdiscloses a device where energy is absorbed by friction which isgenerated in a reciprocating piston and cylinder arrangement. Asignificant drawback to this type of restraint is the large amount ofvariability in the resulting frictional forces, which providesinconsistent energy absorption.

Still another type of energy absorbing restraint incorporatesmulti-strand helical cables trapped between plates which function as aspring to allow for thermal expansion. Devices using such an arrangementare disclosed, for example, in U.S. Pat. Nos. 4,190,227, to Belfield etal., entitled "Vibration Isolator And Method For Manufacturing Same,"and 4,783,038, to Gilbert et al., entitled "lsolator Apparatus."

These devices absorb energy by the rubbing and sliding of cable strandswhen such strands are subjected to dynamic displacements. The energyabsorbing component of such devices is known as a wire rope isolator.

U.S. Pat. No. 5,240,232, to Loziuk, entitled "Pipe Restraint," whichpatent is commonly assigned herewith, discloses wire rope isolatorsincorporated into a pin-pin device for connection between, for example,a process pipe and a structure.

That device uses wire rope isolators which trap or clamp the wire cablebights (i.e., coils) at about 180° degrees apart. Such devices, however,typically require centering bushings or slide plates to maintain themoving portions of the device coaxial, one relative with the other.

Accordingly, it is advantageous to have a device which uses wire ropeisolators configured so as to eliminate the need for centering bushingsor slide plates, which device maintains the moving portions of thedevice coaxial, one relative with the other.

SUMMARY OF THE INVENTION

The present invention provides a wire cable isolator that connects toand isolates a device from an adjacent structure or support member wherethe device is subject to movement due to dynamic loads and/or thermalexpansion. The isolator is of a simple construction, that provides easeof inspection and minimal maintenance.

The isolator has predetermined, symmetrical force-deflection properties.The wire cable isolator includes first and second pairs of entrapmentmembers and a wire cable formed in a spiral. The cable has at least onebight.

The spiral has an externally unloaded shape which is maintained by thefirst and second pairs of entrapment members. The first pair ofentrapment members clamp the wire cable spiral at opposite side of thewire cable spiral and the second pair of entrapment members clamp thewire cable spiral at opposite side of the wire cable spiral. The firstand second pairs of entrapment members are disposed at predeterminedpositions about an exterior periphery of the spiral.

In a preferred embodiment, the first pair of entrapment members clampthe wire cable spiral at 180° one with the other, and the second pair ofentrapment members clamp the wire cable spiral at 180° one with theother. In a most preferred embodiment, the first and second pairs ofentrapment members are disposed 90° one with the other.

Preferably, each entrapment member includes an inner clamping plate andan outer clamping plate. Each inner clamping plate is secured to itsassociated outer clamping plate with the wire cable disposed or capturedtherebetween.

The isolator may be used in an energy absorbing and displacementlimiting device, such as a restraint. Such a restraint is used forconnecting an object subject to movement due to dynamic loads andpossibly thermal deflection, such as a pipe, and an adjacent structure,such as a building or a support member.

The restraint which incorporates the isolator has symmetrical stiffnessproperties in both tension and compression, and resists buckling underload.

The restraint includes a first, inner cylinder having an extension tubemounted to one of the ends of the cylinder, and a second, outer hollowcylinder. The second hollow cylinder surrounds the first, innercylinder. A wire cable isolator is mounted to the inner cylinder by onepair of entrapment members, and is mounted to the outer cylinder by theother pair of entrapment members.

In one embodiment of the restraint, the isolator is mounted in anannulus manner. That is, the isolator is mounted between the inner andouter cylinders. This embodiment may includes viewing ports in the outercylinder for visually inspecting the isolator in place.

In an alternate embodiment, the isolator is mounted external of theouter cylinder.

These and other features and advantages of this invention are evidentfrom the following description of the preferred embodiments of thisinvention with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of a quarter-loop wire cable isolatorembodying the principles of the present invention;

FIG. 1a is a front elevational view of the quarter-loop wire cableisolator of FIG. 1;

FIG. 2 is a side elevational view of an embodiment of a restraintdevice, with a portion thereof broken-away, illustrating a quarter-loopisolator of the present invention assembled within the annulus of twotelescoping, coaxial cylinders;

FIG. 3 is a side elevational view of another embodiment of a restraintdevice, with a portion thereof broken-away, illustrating a quarter-loopisolator of the present invention assembled about two telescoping,coaxial cylinders;

FIG. 4 is a cross-sectional view of the restraint device taken alongline 4--4 of FIG. 3 in the direction indicated;

FIG. 5 is a cross-sectional view of the restraint of FIG. 2 with aportion thereof broken away; and

FIG, 6 is a cross-sectional view of the restraint device taken alongline 6--6 of FIG. 5 in the direction indicated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the present invention is susceptible of embodiment in variousforms, there is shown in the drawings, and will hereinafter bedescribed, presently preferred embodiments with the understanding thatthe present disclosure is to be considered an exemplification of theinvention and is not intended to limit the invention to the specificembodiments illustrated.

With reference now to the figures, and particularly to FIGS. 1 and 2,there is shown a quarter-loop wire rope or wire cable isolator 10 of thepresent invention. The isolator includes a wire cable 12 which is formedin a spiral, having a generally circular or near circular shape. It isto be understood, however, that the wire cable 12 can be formed in avariety of shapes, such as an ellipse or the like, without departingfrom the teachings of the present invention.

The wire cable 12 preferably is formed of individual strands of wire,which are twisted to form the wire cable 12. The wire cable 12 has apredetermined gauge or diameter, discussed in detail herein.

Wire cable is typically formed of single wires which are wound ortwisted together to form a cable strand, and a group of cable strandswhich are wound or twisted together to form a wire cable. Referenceherein to the wire cable count is to the total number of wires in thewire cable. Reference to the wire strand wind is to the number of wiresin each cable strand and the number of cable stands forming the cable.

For example, a wire cable that has a wire strand wind of 7×7 is formedof 7 cable strands, each strand being formed of 7 wires. The count, ortotal number of wires forming the cable, of such a 7×7 wire cable is 49.

As FIGS. 1 and 2 illustrate, the isolator further includes a first pairof entrapment members 14, 16, and a second pair of entrapment members18, 20. Each entrapment member 14, 16, 18, 20, includes a respectiveinner clamping plate 14a, 16a, 18a, 20a, and a respective outer clampingplate 14b, 16b, 18b, 20b.

The first pair of entrapment members 14, 16, clamp or capture the wirecable 12 at opposite sides of the spiral, and the second pair ofentrapment members 18, 20, clamp or capture the wire cable 12 atopposite sides of the spiral. Preferably, entrapment members 14, 16clamp the spiral at 180° one with the other, and entrapment members 18,20, clamp the spiral at 180° one with the other.

The first pair of entrapment members 14, 16, and the second pair ofentrapment members 18, 20, are disposed at predetermined positions aboutan exterior periphery of the spiral. Preferably, the first pair ofentrapment members 14, 16, and the second pair of entrapment members 18,20, are disposed 90° one with the other.

As best seen in FIG. I with reference to the first pair of entrapmentmembers 14, 16, each of the clamping plates 14a,b, 16a,b, 18a,b, 20a,b,has a plurality of semicircular notches 22 formed laterally therein forreceipt of the wire cable 12. The notches 22 of each of the innerclamping plates 14a-20a, are aligned with the associated notches 22 ofits respective outer clamping plate 14b-20b. This arrangement forms agenerally circular bore through the plates 14a,b-20a,b, for receivingand securing, or capturing, the wire cable 12.

The inner plates 14a-20a, and outer plates 14b-20b are secured togetherwith suitable fasteners, such as with threaded bolts 24. The bolts 24extend through bores 26 in the respective outer plates 14b-20b, andengage threaded bores 28 in the respective inner plates 14a-20a.Additional mounting bores 30 are provided at locations along theentrapment members 14, 16, 18, 20, as will be further discussed herein.

The isolator 10 exhibits certain force-deflection properties or"stiffness". That is, as forces are placed on the isolator 10 in variousdirections, the wire cable 12 deflects and exhibits it own responsiveforces.

The force deflection properties of the isolator 10 are a function of thespecific configuration of the isolator 10 and the type and size of wirecable 12 used. Some of the design considerations for the cable 12include the material, size and thickness of the wire cable 12. Designconsiderations for the isolator 10 include the pitch of the loops (i.e.,the angle of the cable relative to the longitudinal axis of the isolator10) of the spiral of cable 12, the loop diameter, and the number ofloops (or bights) in the isolator 10,

As will be recognized by those skilled in the art, given thecombinations possible in the design of the isolator 10 and the cable 12,the isolator 10 can be used in a wide range of situations where dynamicloads must be accommodated in particular systems designs. Such systemsmay include piping systems and mounting/isolation systems for devicessuch as electronic devices.

One device in which the isolator 10 of the present invention is used isan annulus-mounted, pin-pin type of pipe restraint 40 as shown in FIGS.2, 5 and 6. The annulus-mounted restraint 40 includes an outer, hollowcylinder 42, an inner cylinder 60 assembled in a telescopic manner, andan isolator 10 disposed therebetween.

The outer, hollow cylinder 42 includes a pair of end caps 44, 46 ateither end of the cylinder 42. The end cap 44 has a threaded bore 45therethrough for receiving a threaded rod 48 that may include anenclosed rod end 50 for securing the restraint 40 to a structure or to apipe or the like. A threaded jam nut 52 may also be provided to preventthe rod 48 from disengaging from the end cap 44.

The opposing end cap 46 has a bore 54, generally centrally therethrough.The end caps 44, 46, may be sealed to the outer cylinder 42 in anysuitable manner, as by welding, by threaded connection, or by fasteners(not shown).

The outer cylinder 42 also includes mounting holes 56 positioned alongits length at locations which align with the mounting bores 30 of theisolator 10. The outer cylinder 42 may also include inspection ports 58positioned along its length for visually inspecting the isolator 10.

The inner cylinder 60 is disposed within the interior of, and coaxialwith, the outer cylinder 42. The inner cylinder 60 preferably is hollowto minimize the weight of the restraint 10.

The inner cylinder 60 includes an end cap 62 and an extension tube 64extending therefrom. When the inner cylinder 60 is mounted coaxially inthe outer cylinder 42, the extension tube 64 extends through the bore 54in the end cap 46.

The extension tube 64 includes a threaded bore 66 at one end, whichthread is opposite that of the thread in bore 45 of end cap 44. Theopposing threads allow the restraint to be fitted in place, by turning,similar to the fitting of a turnbuckle.

The restraint 40 includes a threaded rod 68 which threadedly engagesextension tube 64. The rod 68 may include an enclosed end 70 and a jamnut 72 to prevent the rod 68 from disengaging from the threaded bore 66.

The inner cylinder 60 further includes mounting bores 74 therein formounting the isolator 10 thereto.

In order to prevent the wire bights from excessive displacement, the endcaps 44, 46, provide internal stops to the restraint 40.

In assembling the restraint 40, an appropriate isolator 10 is choseninto which the inner cylinder 60 is placed. To mount the cylinder 60 tothe isolator 10, two opposing entrapment members, such as the first pair14, 16, are bolted to the cylinder 60 using suitable fasteners such asthe bolts 76, which engage the mounting bores 30.

The inner cylinder 60, extension tube 64, and the isolator 10 then areplaced into the outer cylinder 42, with the extension tube 64 extendingthrough bore 54. The isolator 10 then is mounted to the outer cylinder42 by the second pair of entrapment members 18, 20, which are at apredetermined position about an exterior periphery of the spiral.Preferably, the first pair of entrapment members 14, 16, and the secondpair of entrapment members 18, 20, are 90° apart one from the other. Inthe present example where the entrapment members 14, 16, are mounted tothe inner cylinder 60, the entrapment members 18, 20, are mounted to theouter cylinder 42. The isolator 10 is mounted to the outer cylinderusing suitable fasteners such as the bolts 78.

The threaded rods 48, 68, and as necessary the jam nuts 52, 72, are thenassembled to the restraint 40. The approximate overall length of therestraint 40 required for a particular application is determined by thelength of the extension tube 64. The restraint 40 can be furtherlengthened or shortened prior to installation to meet the requirementsof the particular installation by adjusting the length of the threadedrods 48,68 external of the restraint 40. Once installed, the restraintload is adjusted by rotating the restraint 40 about its longitudinalaxis to threadedly engage the rods 48, 68, in a turnbuckle-like manner.

FIGS. 3 and 5 illustrate an alternate embodiment of a restraint 90 whichuses the present quarter-loop isolator 10. The restraint 90 is anexternally-mounted, pin-pin type of restraint where the isolator 10 ismounted externally of an outer cylinder 92, which is mounted about orexternally of an inner cylinder 94 in a telescopic manner. Thisconfiguration allows for ease of inspection of the isolator 10.

The inner cylinder 94 of this embodiment is similar to the innercylinder of the annulus-mounted configuration of the restraint 40 ofFIGS. 2, 5, and 6. The outer cylinder 92 of this embodiment has a pairof channels or openings 96 which extend longitudinally along a portionof the cylinder 92.

The isolator 10 is mounted to the inner cylinder 94 using a pair ofextension blocks or spacers 98 which are disposed intermediate theentrapment members (such as the first pair 14, 16) and the body of thecylinder 94. The extension blocks 98 have a thickness at least equal tothe thickness of the outer cylinder 92. The isolator 10 is mounted tothe inner cylinder 94 using suitable fasteners such as the bolts 100.

The inner cylinder 94 and the isolator 10 then are assembled to theouter cylinder 92. The inner cylinder 92 is disposed in the outercylinder 92 such that the extension blocks 98 slidably move through thechannels 96. This configuration allows the inner cylinder 94 to slidablymove back and forth within the outer cylinder 92. The isolator 10 ismounted to the outer cylinder 92 in a suitable manner, such as by thebolts 102.

In order to prevent excessive displacement of the wire bights, internalstops are provided. The internal stops are provided in the compressionand tension modes of the restraint 90 by contact between the extensionblocks 98 and the channels 96. Alternatively, in the compression mode, astop is provided by the end cap 111.

Similar to the annular restraint 40, the externally-mounted restraint 90includes threaded rods 104, 106, each rod having a closed end 108, 110.The rods 104, 106, may be fitted with jam nuts 112, 114 to prevent therods 104, 106 from disengaging from the cylinder 92 and the end cap 111,respectively. The externally-mounted restraint 90 is adjustable prior toinstallation and subsequent thereto by rotating the restraint 90 aboutits longitudinal axis similar to the adjustment of restraint 40. Eitherrestraint 40, 90 can be preloaded, that is, it can be subjected to astatic load, by rotating the restraint 40, 90, in a turnbuckle-likemanner after it is installed.

In either embodiment, the restraint 40, 90 is used to control dynamicmotion of an object, such as a pipe, in a direction along the centralaxis of the restraint 40, 90. Movement is controlled by connecting therod end 50, 108 to the object and connecting the opposing rod end 70,110 to a structure such as a building or member support.

As the object is displaced, such as by dynamic forces, the innercylinder 60, 94 moves along its central axis relative to the outer,hollow cylinder 40, 92. This motion is resisted by the spiral of wirecable 12 which is connected to inner cylinder 60, 94 and outer hollowcylinder 40, 92. The stiffness characteristics of the isolator whichprovide the forces which resist movement are a function of variousfactors, including the material, size, and thickness of the wire cable12, and geometric parameters of the isolator including the pitch of theloops of spiral of the cable 12, the loop diameter and number of loops(or bights) in the isolator 10.

As the wire cable 12 is deflected, the individual strands of wire whichmake up the wire cable 12 bundle rub against each other resulting infrictional hysteresis. Such frictional hysteresis results in the dynamicmotion of the object being damped out.

The present invention thus provides a spring-dashpot type device whichis of simple construction with minimal, if any, maintenancerequirements. When necessary to meet the requirements of the particularinstallation, a restraint may be constructed to allow for visualinspection of the wire cable 12 by providing inspection ports 58 in theouter cylinder 42, such an arrangement being exemplified by the annulusrestraint 40, disclosed herein.

Alternately, as exemplified by the externally-mounted restraint 90, thewire cable 12 can be configured about or external to the outer cylinder92. This configuration provides maximum inspection capabilities of thewire cable 12. In either embodiment 40, 90, protection of the energyabsorbing wire cable 12 is afforded by limiting the deflection to whichthe cable 12 may be subjected.

It is to be noted that the present restraints use telescoping, coaxialcylinders. This configuration provides for efficient use of thestructural members when the restraints are loaded in axial compression.Other configurations, however, may also be used.

From the foregoing it will be observed that numerous modifications andvariations can be effectuated without departing from the true spirit andscope of the novel concepts of the present invention. It is to beunderstood that no limitation with respect to the specific embodimentsillustrated is intended or should be inferred. The disclosure isintended to cover by the appended claims all such modifications as fallwithin the scope of the claims.

What is claimed is:
 1. A wire cable isolator of simple construction,ease of inspection and minimal maintenance to connect to, and isolate adevice subject to movement due to dynamic loads, from an adjacentstructure, the wire cable isolator having predetermined, symmetricalforce-deflection properties, the wire cable isolator comprising:firstand second pairs of entrapment members, each said entrapment memberincluding an inner clamping plate and an outer clamping plate securedone to the other; and a wire cable formed in a spiral having at leastone bight, said spiral having an externally unloaded shape maintained bysaid first and second pairs of entrapment members, said cable beingcaptured between said inner clamping plate and said outer clamping plateof each said entrapment member, said first pair of entrapment membersclamping the wire cable spiral at opposite sides of the wire cablespiral, and said second pair of entrapment members clamping the wirecable spiral at opposite sides of the wire cable spiral, said first andsecond pairs of entrapment members being disposed at predeterminedpositions about an exterior periphery of said spiral.
 2. The wire cableisolator of claim 1, wherein said first pair of entrapment members clampthe wire cable spiral at 180° one with the other, and said second pairof entrapment members clamp the wire cable spiral at 180° one with theother, said first and second pairs of entrapment members being disposed90° one with the other.
 3. The wire cable isolator of claim 1, whereinsaid wire cable has a predetermined diameter, a predetermined count, anda predetermined wire strand wind, and said force-deflection propertiesof the wire cable isolator are determined by at least one of saidpredetermined diameter, said predetermined count, and said predeterminedwire strand wind.
 4. The wire cable isolator of claim 1, wherein saidwire cable spiral has a predetermined pitch angle, and saidforce-deflection properties of said wire cable isolator are determinedby said pitch angle of said wire cable spiral.
 5. The wire cableisolator of claim 1, wherein said bight has a predetermined diameter,and said force-deflection properties of said wire cable isolator aredetermined by said bight diameter.
 6. The wire cable isolator of claim1, wherein said wire cable isolator includes a plurality of bights, andsaid force-deflection properties of said wire cable isolator aredetermined by the number of said bights.
 7. A wire cable isolator ofsimple construction, ease of inspection and minimal maintenance, toconnect to and isolate a device subject to movement due to dynamic loadsfrom an adjacent structure, the wire cable isolator havingpredetermined, symmetrical force-deflection properties, the wire cableisolator comprising:first and second pairs of entrapment members; and awire cable formed in a spiral having at least one bight and having anexternally unloaded shape maintained by said first and second pairs ofentrapment members said entrapment members of said first and secondpairs of entrapment members clamping the wire cable spiral at at leastfour predetermined spaced positions about an exterior circumferentialperiphery of said spiral.
 8. The wire cable isolator of claim 7 whereinsaid entrapment members are located at four predetermined positionsabout said exterior circumferential periphery of said spiral, each beingpositioned about 90° relative to its adjacent entrapment members.
 9. Thewire cable isolator of claim 7 wherein each entrapment member includesan inner clamping plate and an associated outer clamping plate securedthereto, wherein said cable is captured between each said inner clampingplate and its associated outer clamping plate.